Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/818d2fc7295c527d0631e9c59256ba3b.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563